Process control systems, such as those used in chemical, petroleum, pharmaceutical, pulp and paper, or other manufacturing processes, often include a backup or safety system to ensure operation of or to remove power from one or more field devices in the event of a malfunction of a primary system. Field devices, which may be, for example, device controllers, valves, valve actuators, valve positioners, switches and transmitters (e.g., temperature, pressure, flow rate, and chemical composition sensors) or combinations thereof, perform functions within the process control system such as opening or closing valves and measuring or inferring process parameters. During an emergency, power may be removed from the field devices.
Known safety instrumented process control systems typically include a controller of an input/output (I/O) card having multiple channels. When power is to be removed from a field device coupled to one of the channels of the I/O card, a group shutdown of all of the channels is required. To mitigate the effect of a group shutdown, I/O cards are typically deployed in redundant pairs. However, a failure on a single channel on either one of the cards in the redundant pair prevents the removal of power from a field device, which reduces the overall safety of the system.